The invention relates to a head gasket to be installed between two engine members, such as a cylinder head and a cylinder block, to seal therebetween.
More specifically, the present invention relates to a head gasket having high sealing ability and good durability even in an area outside an area surrounded by bolt holes or bolts for tightening the cylinder head and the cylinder block.
In case joint surfaces between the cylinder head and the cylinder block (cylinder body) of an engine of an automobile are sealed, a head gasket is installed therebetween to thereby seal combustion gas.
In view of the demand of light weight and low cost of the engine, the head gasket has been changed to a metal gasket having a simple structure of one or two metal plates from a laminate type gasket having a plurality of metal plates. Since the number of the constituting plates is reduced, the material to be used has been limited.
Therefore, in the laminate-type gasket formed of the plural metal plates, although a bead, grommet and shim, which can be used as a sealing device, are combined as desired and provided in double, in the laminate-type gasket formed of a few plates, the kind and number of sealing devices are limited, so that simplified sealing devices have to be used. Moreover, the area which can be used for the sealing devices is reduced due to making the compact engine.
The head gasket, as shown in FIG. 4, is formed in conformity with a shape of an engine member, such as a cylinder block, and provided with holes 2 for the cylinder bores (hereinafter referred to simply as xe2x80x9ccylinder borexe2x80x9d), liquid holes 3 for circulating cooling water and engine oil (hereinafter referred to simply as xe2x80x9cliquid holexe2x80x9d), holes 4 for the bolts (hereinafter referred to simply as xe2x80x9cbolt holexe2x80x9d) and the like. Then, beads 12, 13 as the sealing devices are disposed around the holes 2, 3 to be sealed, respectively.
Although the sealings are carried out by the same gasket between the same engine members, the sealing abilities required by the respective holes to be sealed are greatly different. In the cylinder bore 2, it is required to seal the combustion gas of high temperature and high pressure in the cylinder bore, while in the liquid hole 3, it is required to seal a liquid of relatively low temperature and low pressure.
With respect to the cylinder bore 2, the base plate for sealing that portion is made of an annealed stainless material or soft steel material excellent in heat resistance and the bending ability. Also, around each cylinder bore 2, there is provided a bead 12 capable of coping with the high temperature and high pressure, and having a good elasticity with a circular arc shape and a narrow width, which provides a good follow-up ability with respect to changes of spaces. Also, the cylinder bore 2 is surrounded by the bolt holes 4 for tightening the cylinder head and the cylinder block with the bolts to thereby obtain a large surface pressure by the tightening force.
While the bead 13 is provided around the liquid hole 3 to seal therearound, due to the structure of an engine, there is a case where the liquid hole 3 is located at an area B outside an area A surrounded by the bolt holes 4.
In this case, pressing force by the tightening bolts is acted on only one side of a portion for sealing the liquid hole 3, so that the surface pressure becomes small. To cope with the problem, it has been practiced that the height of the bead is made high, the width of the bead is made narrow, or the shape of the bead is made sharp.
However, in the area B outside the area A surrounded by the bolt holes 4, since only one side is fixed by the tightening bolts and the other side is not supported, a space between the cylinder head and the cylinder block is greatly changed by the cooling-heating temperature cycle through the operation of the engine.
Therefore, in case the portion for sealing the liquid hole 3 disposed in the area B outside the area A is made of the same metal material as that of the base plate for making a normal gasket, the follow-up ability with respect to the changes of the space becomes poor even if the shape of the bead is specially designed for it. Also, in case the gasket receives a great change, the gasket is liable to be subjected to creep relaxation. Thus, there has been a problem such that the sealing ability and durability with respect to the liquid holes 3 are not sufficient.
More specifically, since a deformable property with respect to the heat resistance and the bending ability is required in order to seal combustion gas of high pressure and high temperature around the cylinder bore 2, a material excellent in heat resistance and bending ability, such as annealed stainless material and soft steel material, is preferable. However, in the portion where a great change takes place at the time of the cooling-heating temperature cycle, a material capable of following up the change with an appropriate elasticity, such as a spring steel material, is preferable. Especially, in the area B outside the area A surrounded by the bolt holes 4, it is preferable to use the spring steel material.
However, with a structure wherein the entire base plate is made of the same metal material as in the conventional gasket, the above-stated both conditions can not be satisfied.
In view of the above problems, the present invention has been made and an object of the invention is to provide a head gasket having a thin plate structure, wherein in case joint surfaces of a cylinder head and a cylinder block of an engine are sealed by a metal head gasket, a cylinder bore in an area surrounded by bolt holes and a liquid hole disposed outside the area are both sealed by optimum metal materials, respectively, to thereby provide a head gasket having a good sealing ability and durability.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above object, a head gasket according to the present invention seals between a cylinder head and a cylinder block of an engine, and a base plate of the head gasket is generally made of a first metal material, such as annealed stainless material or soft steel material. A circumferential member made of a second metal material, such as a spring steel material, is disposed to a portion for sealing a liquid hole formed in an area outside the area surrounded by the bolt holes for tightening the cylinder head and the cylinder block by bolts, and a bead surrounding the liquid hole is provided on the circumferential member. The circumferential member is integrally joined to the base plate.
In the above head gasket, it is preferable that a Vickers hardness of the first metal material is in a range of 70-200, and a Vickers hardness of the second metal material is in a range of 300 to 600.
In the head gasket, the circumferential member and the base plate are linearly integrated by the laser welding.
More specifically, as the first metal material for constituting the base plate, there are considered an annealed stainless material, soft steel material and the like having a small Vickers hardness, good heat resistance and bending ability, while as the second metal material for constituting the circumferential member, there are considered a spring steel material and the like having a large Vickers hardness and good elasticity. However, a combination of an annealed stainless material or soft steel material and a spring steel material is most preferable.
According to the structure, since the base plate for sealing the cylinder bores and covering portions compressed by the tightening bolts is made of the first metal material, such as annealed stainless material or soft steel material, having a Vickers hardness of 70-200, good sealing ability with respect to the cylinder bores and good fitness with the cylinder head, cylinder block and the like can be obtained.
Since the circumferential member for sealing the liquid holes disposed on the area outside the area surrounded by the bolt holes is made of the second metal material, such as the spring steel material, having the Vickers hardness of 300-600, preferably 350-450, even in the outside area where the change of space between the cylinder head and the cylinder block becomes large due to a vibration caused by the cooling-heating temperature cycle at the time of operation of the engine, the follow-up ability due to the elasticity of the second metal material is improved. Thus, the sealing ability and durability with respect to the liquid holes disposed on the area outside the area surrounded by the bolt holes can be improved.
In case the circumferential member and the base plate are joined, spot welding margins may be provided on the end portions of the circumferential member and the base plate, respectively, and the spot welding margins may be partially overlapped with each other and spot-welded. However, it is preferable that a joining portion is formed in a linear shape by the laser welding.
In case the circumferential member and the base plate are joined in the linear shape, since a laminating structure of the circumferential member and the base plate is not employed, the weight of the head gasket can be reduced as well as the material thereof is saved. Further, by welding the circumferential member and the base plate in the linear shape, the joining strength can be extremely improved when compared with the spot welding, so that even in case the vibration is relatively large and the circumferential member is supported only by one side, the fatigue failure is hard to occur.
Incidentally, the above described structure according to the present invention is especially effective when the number of the base plate of the metal gasket is one. However, even in case the number of the base plates is plural or the number of the base plates is more than two, i.e. a metal laminate gasket includes an intermediate plate, i.e. more than two, good effect can be obtained.
Also, the difference between the elastic coefficients of the base plate and the circumferential member may be made by the heat treatment process by locally carrying out a heat treatment, in addition to the joint of different metal materials.